Now that U.S. intelligence officials have confirmed that a surface-to-air missile shot Malaysia Airlines flight MH17 from the sky over eastern Ukraine on Thursday afternoon, the region’s combatants are trading accusations about whose missile it was.

No one is so far willing to claim credit for the conflict’s first mass-casualty attack on international civilians. There were 295 people aboard the flight; Malaysia Airlines has confirmed that they included Dutch and British citizens, as well as Australians, Malaysians, Indonesians, Canadians, and Filipinos. (Update 7/18: the number is now being reported as 298.) So far, one American citizen, who also held Dutch citizenship, has been confirmed killed in the crash.

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Ukrainian president Petro Poroshenko called the crash “a terrorist act” and insisted that “the Ukraine armed forces did not fire at any targets in the sky.” Meanwhile, the official Russian news organization RIA Novosti quoted the head of Russia’s Federal Air Transport Agency as saying that “the responsibility [for flight safety] falls on the Ukrainian side.” (Bracketed insertion RIA Novosti’s.) Alexander Boordai, the leader of the Donetsk People’s Republic, the self-declared breakaway region in eastern Ukraine, made a more explicit accusation: “It was either Ukrainian aviation or anti-missile defense” that downed the plane. Ukraine’s rebel militias, he said, simply didn’t have the capability to take down a civilian airliner flying at MH17’s altitude.

Given that MH17 was reportedly flying at 33,000 feet when it was shot down, such an attack would indeed represent a major feat for a nonstate actor. There are historical precedents for civilian aircraft being shot down by missiles, but one reason it’s a relatively rare occurrence is that the necessary capabilities tend to be under the control of governments. “There aren’t that many insurgent groups that have that kind of a capability,” says Max Abrahms, a terrorism specialist and professor of political science at Northeastern University.

“But in this case, it actually makes sense” that an insurgent group shot down the plane, he says. States may as a general rule have better weapons than insurgent groups, but “really that power asymmetry goes out the window when the nonstate actor has strong backing from a government. Particularly from a government as weaponized as Russia.”

As my colleague Alexis Madrigal has pointed out, it’s at least possible that separatists in eastern Ukraine have the technical capability to down an aircraft flying at 33,000 feet. And the rebels have repeatedly demonstrated the capability to shoot down Ukrainian military aircraft.

But an international civilian target is, obviously, different—which is why all parties are scrambling to blame each other. Abrahms is inclined to attribute the attack to the separatists. However, he says, “this was almost certainly a mistake.”

Whether or not it was a mistake, the incident could set a new precedent on the world’s battlefields. As governments have acquired better and better weapons, and either lost control of them as in Libya or given them away as in Russia, Abrahms says, “the quality of weaponry falling into the hands of these militants has gone way up.”